Presidential candidate Norbert Hofer of the Austrian Freedom Party (FPOe) poses as he casts his ballot at the polling station in his hometown Pinkafeld, Austria, May 22, 2016. REUTERS/Heinz-Peter Bader

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VIENNA (Reuters) - The re-run of Austria's knife-edge presidential election could produce a significantly different result, a poll published on Thursday found, as 17 percent of respondents said they would or might switch sides in a runoff vote that includes the far right.

Freedom Party candidate Norbert Hofer narrowly failed to become the European Union's first far-right head of state when he lost the second-round vote on May 22 to former Greens leader Alexander Van der Bellen by less than one percentage point.

But the Freedom Party (FPO) successfully challenged the result before the Constitutional Court, which found that several rules were broken in the handling of postal votes as officials rushed to count the ballots that eventually swung the election.

Although there have been few suggestions of foul play and candidates' positions are largely unchanged, a Gallup poll for tabloid daily Oesterreich found five percent of respondents said they would vote differently and 12 percent said they might.

The survey of 600 people carried out on Tuesday and Wednesday gave a slight edge to Hofer ahead of the Oct. 2 re-run for the largely ceremonial post, but his lead was within a wide margin of error.

Support for Hofer was between 48.5 percent and 57.5 percent, the mid-point being 53 percent, the poll said. Van der Bellen's backing was between 42.5 and 51.5 percent, or, on average, 47 percent.

Oesterreich did not say how events since the original run-off vote in May have influenced public opinion. Britain's vote to leave the European Union appears to have worried voters, and Van der Bellen has sought to capitalize on Hofer's eurosceptic views.

Militant attacks in Nice and Germany, however, as well as continuing concerns about Europe's migration crisis, are likely to play into the hands of the anti-immigration FPO, which has made law and order one of its central themes.